How do I boost my marks in the longer answer questions?

In A-Level psychology, the longer answer questions are looking for a critical evaluation of the evidence or explanations. Often, the marks will be weighted towards AO3, which requires you to evaluate your evidence, for example, saying that Milgram can evidence obedience is good, but you need to examine the positives and negatives of the study, for example, the ethics and the gender of the sample.